I maintain a research group wiki with a more updated list of research activities, including a list of possible research projects. If you are a prospective student and would like extra details on these projects, please email me to obtain access to the appropriate wiki pages.

Ultra-Faint Dwarf Galaxies Collaborators: J. Simon In the past few years the number of satellite galaxies around the Milky Way has doubled. These newly discovered objects have luminosities similar to the faintest globular clusters, but kinematics and metallicities which firmly suggest that they are dwarf galaxies. We present Keck/DEIMOS spectroscopy for eight of these ultra-faint satellites. All are highly dark matter-dominated with mass-to-light ratios approaching 1000. These ultra-faint dwarf galaxies substantially alleviate the discrepancy between the observed number of Milky Way satellites and that predicted by standard Lambda Cold Dark Matter models. Kinematics of the Ultra-Faint Milky Way Satellites Simon J., Geha M., 2007, ApJ, 670, 313 See the Keck Observatory press release or article in Discover magazine.

SDSS Low Mass Dwarf Galaxies Collaborators: M. Blanton, A. West, M. Masjedi We present results from an radio HI survey of dwarf galaxies selected from the SDSS with rotational velocities between 20 - 80 km/s. These data represent the largest homogeneous sample of low luminosity dwarf galaxies with well-measured HI and optical properties. The Baryon Content of Low Mass Galaxies Geha M., Blanton M., Masjedi M., West A., 2006, ApJ, 653, 240 Testing Cold Dark Matter with the Low Mass Tully-Fisher Relation Blanton M., Geha M., West A., 2007, astro-ph070.3813 Download dwarf galaxy data

NGC 205: An Tidally Interacting Dwarf Elliptical Galaxy Collaborators: P. Guhathakurta, M. Rich, M. Cooper, K. Howley NGC 205 is the nearest example of a dwarf elliptical galaxy and the prototype of this galaxy class. A close satellite of the nearby large spiral galaxy Andromeda (M31), photometric evidence suggests that NGC 205 is gravitationally interacting with its parent galaxy. We have measured the internal dynamics of NGC 205 to significantly larger radius than previously possible by combining the velocity measurements of over 700 individual stars. Internal Dynamics of Local Group Dwarf Elliptical Galaxies I. Mapping the Dynamics of NGC 205 Beyond the Tidal Radius Geha M., Guhathakurta P., Rich R. M., Cooper M. C. 2005, AJ, 131, 332 Unraveling the Interaction of NGC 205 with M31 Howley K., Geha M., Guhathakurta P., Montgomery R., Laughlin G., 2006 in prep.

A Counter-Rotating Core in a Low Luminosity Elliptical Galaxy Collaborators: P. Guhathakurta, R. van der Marel We present evidence for a counter-rotating core in the low-luminosity (M_B = -18.2) elliptical galaxy NGC 770 based on internal stellar kinematic data. This counter-rotating core is unusual as NGC 770 is not the primary galaxy in the region and it lies in an environment with evidence of on-going tidal interactions. We discuss several formation scenarios for this core and favor one in which NGC 770 accreted a small gas-rich dwarf galaxy during a very minor merging event. If this scenario is correct, it represents one of the few known examples of merging between two dwarf-sized galaxies. NGC 770: A Counterrotating Core in a Low-Luminosity Elliptical Galaxy Geha M., Guhathakurta P., van der Marel R.P. 2005, AJ, 129, 2617

Optical Redesign of a Wide-Field Imaging Camera I was involved in a upgrade to an existing instrument at the Las Campanas Observatories in Chile. The Wide-Field CCD (WFCCD) is an imager and multi-object spectrometer in use at the du Pont 100-inch telescope. The previous CCD was a 2048x2048 chip which provides a 25 arcmin diameter field of view sampled at 0.77 arcsec/pixel which undersamples the point spread function and restricts the available field-of-view. Installation of a new 4064x4064 CCD is in progress. The new CCD will provide a slightly larger field-of-view with a smaller pixel size of 0.48 arcsec/pixel. This pixel size is much better matched to both the seeing typical at Las Campanas and the predicted optical performance of the instrument. The WFCCD field-of-view is comparable to that of IMACS on the Magellan telescope and will complement IMACS by providing pre-imaging capability for multislit spectroscopy work.

Dynamics of Dwarf Elliptical Galaxies Thesis work at UCSC Collaborators: P. Guhathakurta, R. van der Marel Dwarf elliptical galaxies are the most abundant galaxy type found in the nearby universe. As part of my PhD thesis, we have obtained Keck ESI spectroscopy of 18+ Virgo cluster dwarf ellipticals. Velocity and velocity dispersion profiles have been measured out to 1 kpc. We have modeled the stellar kinematics of these galaxies, putting constraints on central black hole mass, and will soon begin modeling their stellar populations. To compare the kinematics of dEs in varying environments, we have recently observed five satellites of isolated spiral galaxies, morphologically identified as dwarf ellipticals. Internal Dynamics, Structure and Formation of Dwarf Elliptical Galaxies: II. Rotating Versus Non-Rotating Dwarfs Geha, M., Guhathakurta, P., van der Marel, R., AJ, 2003, 126, 1794 Internal Dynamics, Structure and Formation of Dwarf Elliptical Galaxies: I. A Keck/HST Study of Six Virgo Cluster Dwarfs Geha, M., Guhathakurta, P., van der Marel, R., AJ, 2002, 124, 3073

Quasars behind the Magellanic Clouds Collaborators: K. Cook, T. Axelrod, C. Alcock, A. Drake and the MACHO Collaboration The goal of this project is to identify a robust set of quasars behind the Magellanic Clouds for proper motion measurements. We have developed a technique to select quasar candidates from the stellar foreground using aperiodic variability in the MACHO database. Follow-up spectroscopy with the AAT+2dF and ANU's 2.3m telescopes have revealed over 50 previously unknown quasars at redshifts between 0.1 to 2.5. These quasars will serve as invaluable tools in studying the orbital motion of the Magellanic Clouds and consequently the size and shape of our Milky Way. Variability-Selected Quasars in MACHO Project Magellanic Cloud Fields Geha, M. and the MACHO collaboration, AJ, 2003, 125, 1 The Proper Motion of the Large Magellanic Cloud using HST Kallivayalil N., van der Marel R.P., Alcock C., Axelrod T., Cook K.C., Drake A.J., Geha M. 2005, AJ, astro-ph/0508457 Download quasar data (last update Sept 2002)

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